1. Technical Field
The invention relates to vibration damping devices which develop damping performance when applied between two moving members such as automobile suspensions or other equipment. More particularly, the invention relates to a damping device using an electrorheological (ER) fluid as the damping medium which uses two piston-rod guide-assemblies for supporting both ends of the piston rod and positioned so the sliding surfaces are not immersed in the ER fluid and are external to the working chamber of the damper.
2. Background Information
In automotive vehicles, vibrations are caused by traveling over road protrusions or depressions and are transmitted from the tire surface to the vehicle frame. Vibration damping devices have been used to dampen these road vibrations and provide a smoother ride in automotive systems. These shock absorbers are typically oil-filled or high-pressure gas-filled damping devices.
Although conventional oil and high-pressure gas damping devices have proven satisfactory, a more recent development has evolved in which an electrorheological or electroviscous fluid is used within the chamber of the damping device. The liquid is in contact with one or more electrodes, usually mounted in a restrictive passage, which depending upon the size of the electrodes and the amount of voltage applied to the liquid, will change the viscosity of the liquid, enabling the damping device to have an adjustable range of damping characteristics.
Typical automobile dampers, be they electrorheological (ER) dampers or conventional dampers, are axially slidable devices that produce a resistive (damping) force as they are compressed or extended. In practical use they are subjected to, and must be able to withstand, bending forces (side-loads) while retaining axial motion. This necessitates that the slidable members be interconnected at a minimum of two sliding bearing-points. In a conventional damper the slidable members are the damper body or housing and the piston/rod assembly. The corresponding bearing points are the rod-guide assembly and the main piston.
The electrorheological fluids used in ER dampers are most often particle/liquid suspensions. In order to function properly the particles must remain physically intact for the service life of the device. Many known ER dampers are constructed similar to conventional dampers described above, that is the piston is one bearing point and the piston rod the second bearing point. This construction may result in a situation which compromises the integrity of the particles in the ER fluid since one of the bearing points is immersed in the ER fluid. As the damper is cycled, the sliding/rubbing motions of the immersed bearing point subject the particles to forces that may be large enough to damage them. The addition of a bending or side-load force only exacerbates the situation. Should the particles used in the ER fluids be abrasive, the sliding/rubbing motions of the bearing point would erode the metal of the damper body. The resulting inclusion of metallic wear debris in the ER fluid is known to degrade the fluid's performance.
Examples of various prior art dampers using ER fluids are shown in U.S. Pat. Nos. 5,522,481; 5,590,745; 5,598,908; 5,259,487. In these structures the piston is supported at only one end and thus it provides a rubbing action against the inner surface of the piston housing within the ER fluid. Furthermore, the piston rod is only supported at one end with the piston itself being the other space support.
U.S. Pat. No. 5,513,730 shows a usual type of hydraulic damper in which the piston rod is supported at opposite ends of the piston to counteract any unequal loading on the piston and piston rod. However, the sliding surfaces between the piston rod and fixed bearing members in this dual supported shock absorber are exposed to the fluid, which is not a problem when used with standard hydraulic fluids. However, if such a construction is used with an ER fluid, it results in the undesirable abrasion at the sliding surfaces. Thus, the need exists for a simple and effective ER damper that provides spaced supports to the piston to eliminate unequal forces exerted on the piston and/or piston rod, and most importantly avoids contact between the sliding-contact surfaces and the ER fluid contained within the fluid chamber.